1. Field of the Invention
The present invention relates to a CDMA mobile communications system, specifically, to a radio frequency control circuit of a base station of a mobile communications system, which provides call service to a mobile located in a shadow region without establishing a base station in the shadow region.
2. Discussion of Related Art
The radio frequency circuit of a base station of a conventional mobile communications system, as shown in FIG. 1, includes a combiner 1 for receiving carrier signals FA1, FA2, . . . , FAn having the same frequency, which are digital signals modulated, combining them, a power amplifier 2, connected to combiner 1, for amplifying the combined carrier signal, a transmitting antenna 3, connected to power amplifier 2, for radiating the amplified high-power carrier signal toward a communication area, a receiving antenna 4 for receiving a signal sent from a subscriber's mobile, a low noise amplifier 5, connected to receiving antenna 4, for amplifying the received signal with low noise, and a splitter 6 for splitting the amplified signal by frequency allocations. Power amplifier 2 may be configured of a linear power amplifier or high power amplifier.
The operation of the radio frequency circuit of the base station of the conventional mobile communications system is explained below. First, transmission process is performed in a manner that a signal combined with carrier signals FA1, . . . , FAn by combiner 1 is amplified by power amplifier 2, and transmitted to a mobile located in an area other than the shadow region through transmitting antenna 3. The reception procedure is executed in a manner that a radio frequency signal is received from the mobiles located in the area other than the shadow region through receiving antenna 4, amplified by low noise amplifier 5, sent to splitter 6, and inputted to combiner 1 as a carrier signal.
With the radio frequency control circuit of the base station in the conventional mobile communications system, the carrier signal radiated from the transmitting antenna or antenna of the subscriber's mobile is in radio frequency band so that its wavelength is short. This produces the shadow region where the carrier signal cannot be transmitted and received. There are underground, tunnel and the inside of a skyscraper as examples of the shadow region. The shadow region widens as the carrier frequency becomes higher.
Accordingly, the conventional radio frequency circuit cannot provide call service to mobiles located in the shadow region. Furthermore, in order to supply the call service to a subscriber in the shadow region, the base station having the radio frequency circuit must be established each shadow region.